Unitized seals include a pair of stamped metal casings nested together into a unit that can be press fitted into the annular space between a pair of relatively rotatable members, such as bearing races. Internal seals of various types are contained within the space between the nested casings, which may be molded elastomer, usually rubber, or harder, lower friction materials, such as PTFE. Examples may be seen U.S. Pat. No. 5,024,364 to Nash, and in coassigned U.S. Pat. No. 4,497,495 to Christiansen. Typically, the seal runs on a surface of the metal casing, since a rigid, unyielding material, such as metal, is more compatible with a softer material, such as rubber. Still, seals that involve rubber riding on rubber are known, such as that disclosed in U.S. Pat. No. 4,185,838 to Danner.
Two problems that all seals face are seal rubbing friction or torque, especially as additional lines of sealing contact are added, and the rapid fluctuations in the relative locations of the rotatable members that occur in operation, which inevitably causes the relative location of the seals and the surfaces that they run on to fluctuate. Seal friction can be reduced by using lower friction seal materials, such as PTFE disks, instead of rubber. However, PTFE, being a semi-rigid plastic, is less able to rapidly comply fluctuations in its running surface than an elastomer like rubber would be. Rubber, although compliant, is tacky, and, when running on a metal surface, needs some wet lubrication from the bearing grease to reduce its rubbing friction.